Plastic pyrotechnic compositions containing strontium perchlorate and acrylic polymer



United States Patent 3 258 373 PLASTIC rrnorncniuc coMrosrrroNs coN- TAINING STRQNTIUM PERCHLGRATE AND ACRYLIC POLYMER Bernard E. Douda, Bloomfield, Ind., assignor to the United States of America as represented by the Secretary of the Navy No Drawing. Filed July 9, 1964, Ser. No. 381,592 6 Claims. (Cl. 149-19) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to plastic pyrotechnic compositions and more particularly to plastic pyrotechnic composition that are pour castable and upon solidi-fi cation form pyrotechnics that are long burning.

Heretofore, one method ofmanufacturin-g pyrotechnic articles consisted of filling a hollow tube or container with a combustible mixture in powder form and then subjecting the mixture to a very high pressure. The resulting product has a density depending upon various conditions such as the type of mixture and the amount and duration of the pressure applied. Such pyrotechnic articles show wide variations in their rate of combustion.

In order to overcome the disadvantages of compacted pyrotechnic articles, recent developments in the pyrotechnic art has produced various plastic type compounds that can be cast or molded. One such plastic compound is described in US. Patent 2,984,558, which issued May 16, 1961, to Edward Rolle and John Q. Tabor. This patented compound is essentially a mixture of unsaturated polyester resins to which is added a stabilizing ingredient, oxidizers, and a fuel.

In the present invention strontium perchlorate is added to an acrylic monomer. The portion of the strontium perchlorate that dissolves in the acrylic monomer acts as an activator to prepolymerize the acrylic monomer. The undissolved strontium perchlorate remains suspended in solid form in the prepolymerized acrylic monomer. Various fuels, oxidizing agents, and coloring agents are next added to the partially polymerized monomer, and a catalyst is then added to facilitate complete polymerization.

It is therefore a general object of the present invention 'to provide an improved pyrotechnic material which may be readily cast or molded.

Another object of the present invention is to provide a pyrotechnic material which has an essentially constant rate of burning.

A further object of the present invention is to provide a long burning colored flare that can be readily manufactured.

Other objects and advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following description.

It has been found that strontium perchlorate will dissolve in acrylic monomers, such as the esters of acrylic and met-hacrylic acids. At room temperature, about 18 parts of anhydrous strontium perchlorate will dissolve in 100 parts of methyl methacrylate monomer. It has been discovered, however, that the degree of solubility is related to the amount of moisture contained in the oxidant. Maximum solubility occurs when about 2.2 percent of moisture is present in the oxidant. Upon mixing the desired amount of oxidant with the acrylic monomer, prepoly-mer is readily formed, accompanied by heat evolution. This results in an increase in viscosity of the mixture. This reaction occurs without the need of an organic catalyst, and if the process is not regulated as to the degree of solubility and temperature, a hard polymeric mass will be formed. From a production standpoint, this prepolymerization feature is an asset for because of the increase in density and viscosity of the monomer other insoluble ingredients will remain suspended in the viscous blended mass without appreciable settling prior to polymerization.

The strontium perchlorate acts both as an activator and a catalyst in that small amounts of strontium perchlorate when added to an acrylic monomer, will shorten the induction time normally required to polymerize the monomer, and also the temperature required to polymerize the monomer is less. When the strontium perchlorate dissolves in the monomer, there is provided a solution which serves both as a fuel and anoxidizing agent.

The following examples are illustrative of the invention. In each of the examples, the monomer used was methyl methacrylate that was inhibited with 25 p.p.-m. hydroquinone, however, it should be understood, of course, that other esters of acrylic acid and methacrylic acid will work equally as well.

Example I 50 ml. of methyl methacrylate monomer 165 gms. of strontium perchlorate 3 drops of cumene hydroperoxide The ratio, by weight, of monomer to strontium perchlorate is about 1 to 3.5. The mixture was heated in an oven for 12 hours at a temperature of 75 degrees C. A candle was prepared in a fish paper tube having an inside diameter of 1.76 inches, and atwo-inch candle burned for seconds. The flame was about 24 inches high and very bright red in color. A white smoke was produced and there Was, almost no ash.

Example [I 45 ml. of methyl methacrylate monomer gms. of strontium perchlorate 30 gms. of magnesium (atomized) gms. of anhydrous strontium oxalate 10 gms. of anhydrous strontium chloride drop of Lupersol DDM (a solution of 60% methylethylketone peroxide in dimethylphthalate) Example III ml. of methyl methacrylate monomer 50 gms. of strontium perchlorate 50 gms. of magnesium- (atomized) 20 drops of Lupersol DDM The ratio, by weight, of monomer to strontium perchlorate is about 1 to 1.08. The mixture was heated in an oven for 24 hours at a temperature of 75 degrees C. A candle was prepared as in Example I, and the burning time was seconds. The flame was between 12 and 18 inches high and was a. very bright red. A white smoke was produced.

3 Example IV 50 ml. of methyl methacrylate monomer 50 gms. of strontium perchlorate 50 gms. of magnesium (atomized) 30 gms. of strontium carbonate 6 drops of Lupersol DDM The ratio, by weight, of monomer to strantium perchlorate was about 1 to 1.08. The mixture was heated in an over for 24 hours at a temperature of 75 degrees C. A candle was prepared as in Example I and theburning time was 35 seconds. The flame was between 12 and 18 inches high and was a very bright red. A white smoke was produced.

Example V 50 ml. of methyl methacrylate monomer 10 gms. of strontium perchlorate 50 gms. of magnesium (atomized) 40 gms. of strontium nitrate 30 drops of Lupersol DDM The ratio, by weight, of monomer to strontium perchlorate was about 1 to 0.21. The mixture was heated in an oven for 24 hours at a temperature of 75 degrees C. A candle was prepared as in Example I, and the burning time was 22 seconds. The flame was between 12 and 18 inches high and was a very bright red. A white smoke was produced.

Example VI '47 ml. of methyl methacrylate monomer 75 gms. of strontium perchlorate 30 gms. of magnesium (atomized) 15 gms. of aluminum (atomized) 3 drops of Lupersol DDM The ratio, by weight, of monomer to strontium perchlorate was about 1 to 1.7. The mixture was heated in an oven for 24 hours at a temperature of 55 degrees C. A candle was prepared as in Example I and the burning time was 125 seconds. The flame was about 12 inches high and was a very bright red. A white smoke was produced.

Example VII 50 ml. of methyl methacrylate monomer 83.7 gms. of strontium perchlorate 52.3 gms. of magnesium (atomized) 3 drops Lupersol DDM The ratio, by weight, of monomer to strontium perchlorate was about 1 to 1.79. The mixture was heated in an oven for 24 hours at a temperature of 55 degrees C. A candle was prepared as in Example I and the burning time was 110 seconds. The flame was about 12 inches high and was a very bright red. A white smoke was produced.

Example VIII 28 ml. of methyl methacrylate monomer 14 ml. of styrene monomer 90 gms. of strontium perchlorate gms. of magnesium (atomized) 30 gms. of glycine 3 drops of cumene hydroperoxide 4 Example IX 5 6 ml. of methyl methacrylate monomer gms. of strontium perchlorate 25 gms. of magnesium (atomized) 45 gms. of sulfur 10 gms. of anhydrous strontium chloride 2 drops of cumene hydroperoxide The mixture was heated in an oven for-20 hours at 75 degrees C. A candle was made as in Example I and the burning time was 7 minutes.

As can be seen from the foregoing examples, compositions with a high magnesium content burn relatively rapid and are very hot. The addition of sulfur to the mixture increases the burning time, as demonstrated by Example IX. Sulfur is best used in a range of 0.25-0.75 part of sulfur per one part of monomer.

While the foregoing examples list methyl methacrylate as the monomer which is polymerized, strontium perchlorate mixes equally as well when mixed in solution With acrylic acid, methacrylic acid and esters of acrylic acid and methacrylic acid, such as methyl acrylate and ethyl acrylate. Also, while the examples listed above were catalyzed with either cumene hydroperoxide or Lupersol DDM there are many more commonly known catalysts that promote polymerization of acrylic monomers. Included among the known catalysts are diacyl peroxides, ketone peroxides, alkyl hydroperoxides, alkyl peresters, and alkyl acid peresters. Various effects can be obtained by the use of ditferentcatalysts and also combination of catalysts can produce effects not readily available with any single catalyst.

In preparation, the acrylic monomer is normally first mixed with the strontium perchlorate and that portion of strontium perchlorate which dissolves in the monomer causes the monomer to partially polymerize. A portion of the strontium perchlorate will dissolve in the acrylic monomer and, at room temperature, about 18 parts of anhydrous strontium perchlorate will dissolve in parts of acrylic monomer. The partial polymerization of the monomer causes an increase in the viscosity of the mixture and the fuel and other ingredients are then added. The increased viscosity of the mixture prevents the fuel and other undissolved ingredients from settling and consequently, a more homogenous product is produced. Pyrotechnic candles that provide adequate candlepower when burned, and also, that have a long burning time, have been prepared by maintaining a ratio of between 1 and 3.3 parts, by weight, of strontium perchlorate to one part, by weight, of acrylic monomer.

The ratio of fuel to monomer is also critical for military applications in that too small an amount of fuel will result in low average candlepower, while too large an amount of fuel will cause very rapid burning and consequently, too short a burning time. For one red flare, for example, a military specification requires a minimum average candlepower of 20,000 and a minimum burning time of 23 seconds. In order to meet both of these requirements, the ratio of fuel to monomer should be between about 0.2 and 2.0 parts of fuel to one part of acrylic monomer.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood, that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is:

- 1. A consumable pyrotechnic composition comprising:

one part, by weight, of an acrylic polymer, and between one and 3.3 parts, byweight, of strontium perchlorate.

2. A consumable pyrotechnic composition as set forth in claim 1 having uniformly dispersed therein in a finely divided form between 0.2 and 2.0 parts, by weight, of magnesium.

3. A consumable pyrotechnic composition as set forth in claim 1 having uniformly dispersed therein in a finely divided form between 0.2 and 2.0 parts, by weight, of aluminum.

4. A consumable pyrotechnic composition as set forth in claim 1 having uniformly dispersed therein in a finely divided form between 0.2 and 2.0 parts, by weight, of magnesium and between 0.25 and 0.75 part, by weight, of sulfur.

5. A consumable pyrotechnic composition as set forth in claim 1 having uniformly dispersed therein in a finely divided form between 0.2 and 2.0 parts, by weight, of magnesium and between 0.25 and 0.75 part, by weight, of glycine.

6. A consumable pyrotechnic composition comprising: 5

B. R. PADGETT, Assistant Examiner.

one part, by weight, of polymer consisting of two-thirds methyl methacrylate and one-third styrene,

References Cited by the Examiner UNITED STATES PATENTS Rolle et al. Q 149--19 Cobb et al. 14919 Godsey 149-83 Cadwallader 149-19 LEON D. ROSDOL, Primary Examiner. 

1. A COMSUMABLE PYROTECHNIC COMPOSITION EOMPRISING: ONE PART, BY WEIGHT, OF AN ACRYLIC POLYMER, AND BETWEEN ONE AND 3.3 PARTS, BY WEIGHT, OF STRONTIUM PERCHLORATE. 